Yet this negative reactionruns contrary to bipartisan school policy choices over the past two decades. Since the mid-1990s, schools across the United States have hired security guards, many of whom are armed, and stationed police officers in their buildings full time. The New York City public school system alone has a dedicated police force, the NYPD School Safety Division.

This costly, nationwide expansion of police and security is financed by school districts, local police forces, states and even, in part, the federal government, which has provided funds for police-school partnerships since the Clinton administration. The expansion of police into schools over the past 20 years is very popular; there is no political resistance or even a critical dialogue about it in either major party. In my own research, I have found that administrators, teachers and often parents want more police and security guards in their schools.

But the evidence shows that the expansion of police into schools is a flawed policy that can have harmful effects on students. During many research visits, I have spoken at length with police officers stationed at schools full time. I have found almost all of these officers, usually called school resource officers, to be caring individuals. They are willing to let their professional reputations suffer — being a “kiddie cop” is often looked down upon by other officers — in an attempt to help local youths. Many of them mentor students and seek to be positive role models.

But their presence has effects that help transform the school from an environment of academia to a site of criminal law enforcement. Issues that might otherwise be seen as mental health or social problems can become policing matters once an officer is stationed in a school. Arrests for minor infractions, such as fistfights in which there are no injuries, go up. As the 2011 books “Punished” and “Police in the Hallways” have found — among other research — officers can start to see youths as thugs and criminals and begin treating them with hostility and sometimes even abusively. This comes at the expense of students’ rights and their education. Minorities are especially vulnerable to the overpolicing that can take place in schools, which increases both the racial-academic divide and racially skewed arrest rates.

A greater police presence in schools can also increase student offending rates. Research has repeatedly shown that schools can prevent student misbehavior by establishing positive social climates. Students do better when they feel respected and listened to, like a valued part of the school, and when they view school regulations and actions, including security, as fair. Introducing more police into schools can undo these efforts, making what had been an encouraging learning environment, where students are partners in an educational effort, into more of a place where students are subjects of school rules.

The NRA proposal is a bad idea not only because it means more policing but also because it would mean policing by the wrong people. While the presence of police officers in schools can have harmful effects, schools with security guards — particularly armed security guards — fare even worse.

A 2011 study published in the Journal of Police Crisis Negotiations, conducted by researchers at the University of South Florida and Loyola University in New Orleans with data from the National Center for Education Statistics, found that schools with security guards and guards who bear firearms have higher rates of serious violent crime than do similar schools that lack such personnel. Consider also that Columbine High School had armed security guards on staff, and Virginia Tech had a police force, and neither prevented the shootings that occurred there.

There are clear drawbacks to having armed guards in schools. Implementing such a policy would actually put more youth at risk and might divert attention away from a robust discussion of, and progress on, gun control. Instead, we should reconsider our school security policies, drawing on the available evidence of what works and what doesn’t.